Process of polymerizing conjugated dienes in the presence of selected alkyl esters of mercaptyl undecanoic acids as polymerization regulators



Patented Feb. 14, 1950 PROCESS OF POLYMERIZING CONJUGATED DIENES IN THEPRESENCE OF SELECTED ALKYL ESTERS OF MERCAPTYL UNDECA- NOIC ACIDS ASPOLYMERIZATION REGU- LATORS Karl H. Weber, Washington, D. C., assignorto Armstrong Cork Company, Lancaster, Pa., a corporation of PennsylvaniaNo Drawing. Original application March 10, 1944,

Serial No. 525,946. Divided and this application September 17, 1947,Serial No. 774.674

9 Claims. (01. 26082.7)

1 This application is a division of my copending application Serial No.525,946, filed March 10, 1944.

The present invention relates to improvements in the polymerization ofopen chain, aliphatic conjugated dienes containing 4 to 6 carbon atomsin aqueous emulsions and to a new polymerization regulator selected fromthe group consisting of the alkyl esters of ll-mercaptyl undecanoic acidand the alkyl esters of IO-rnercaptyl undecanoic acid.

An open chain, aliphatic conjugated diene containing 4 to 6 carbonatoms, for example, butadiene-1.3, can be polymerized by simple heatingor in an aqueous emulsion. The latter method is preferred as it yieldsproducts which more nearly resemble natural rubber. In general, such aconjugated diene is usually polymerized with a copolymerizable vinylcompound, for example, styrene, as more fully hereinafter set forth. Theemulsion polymerization may result in the formation of products whichare relatively dry and which more nearly resemble vulcanized naturalrubber rather than unvulcanized natural rubber, with the result that thepolymerization products are relatively difiicult to work on the millsand the incorporation therewith of filling materials and the ingredientswhich are necessary for efiecting vulcanization is accomplished withconsiderable difilculty. To overcome these and other disadvantages, ithas been the practice to incorporate in the emulsion a so-calledpolymerization regulator." Dodecyl mercaptan, CmHzsSI-I, is disclosed inU. S. Patent No. 2,281,613 as such a polymerization regulator. Othermercaptans, for example, octyl mercaptan, have also been disclosed aspolymerization regulators, but many of these mercaptans which have beendisclosed have no substantial regulatory effect. A satisfactorypolymerization regulator should produce a synthetic rubber-like materialwhich resembles unvulcanized natural rubber in being relatively plastic,and-in which vulcanizing ingredients may be readily incorporated.

While the exact effect of such regulators is obscure, I believe thatthey tend to give a narrower range of polymer size so that all thepolymers are more nearly the same length. Further. I believe that theytend to reduce cross-linking of the polymers as is evidenced bytheincreased benzene or acetone solubility, though it should be understoodthat I do not intend to be limited to any particular theory.

It is the object of the present invention to provide new compounds whichare useful polymerization regulators, which expedite polymerization ofopen chain, aliphatic conjugated dienes or the polymerization of suchaliphatic conjugated dienes with unsaturated copolymerizable compoundscontaining a vinyl radical, in an aqueous emulsion without undulyretarding the course of the reaction and without involving the formationof undesirable products. Other objects of my invention will become moreapparent from the following description and claims.

I have discovered that the alkyl esters of either 10 or ll-mercaptylundecanoic acid are desirable polymerization regulators for thepolymerization in aqueous emulsion of open chain, aliphatic conjugateddienes containing 4 to 6 carbon atoms. In most cases, an amount of lessthan about 1% of the polymerization regulator (calculated on the totalweight of the monomeric polymerizable ingredients) is suflicient toexert the desired effect. In general, I have found that from about 0.3%to about 0.5% of these polymerization regulators is sufficient. Toogreat an amount of regulator tends to unduly slow down the rate ofpolymerization and too small an amount of regulator will not besuiflciently effective, though it will be understood that the amount ofregulator used with a particular formulation will depend at least inpart upon the materials being polymerized or copolymerized and upon thecharacteristics desired in the final product. The most desirable amountof polymerization regulator for any particular formulation will bereadily apparent to one skilled in the art.

My polymerization regulators may be employed with any open chain,aliphatic conjugated diene containing from 4 to 6 carbon atoms; may beemployed with mixtures of such dienes; or may be employed with a mixtureof one or more such dienes with one or more copolymerizable compoundscontaining a vinyl radical. The term open chain aliphatic conjugateddiene containing from 4 to 6 carbon atoms is intended to includebutadiene-1,3 and the homologues and derivatives of butadiene-1,3 suchas isoprene, 2,3 dimethyl butadiene, chloroprene, bromoprene. iodoprene,and the like.

The term "copolymerizable compound containing a vinyl radical" isintended to include all compounds containing the group CH2 -C which maybe copolymerized with such a diene in an aqueous emulsion. For example,the copolymerizable compounds include styrene, alpha-methyl styrene,alpha-methyl-para-methyl styrene, acrylonitrile, methyl methacrylate,the vinyl esters of the higher fatty acids such as the vinyl esters ofthe acids obtainable by saponification of a drydecanoate, smcmmcoocim.and ethyl mercaptyl undecanoate,

CHaSHCH(CH2) sCOOCzHs have been found to be particularly desirablepolymerization regulators.

My new polymerization regulators may be prepared in any suitable manneror may be prepared as hereinafter described. Unless otherwise set forth,all parts and percentages are by weight.

Hydrogen bromide was bubbled through a solution of 44.7 grams ofundecylenic acid,

CHFCH(CH2) aCOOI-I in heptane to form 43 grams of quite pure l1- bromoundecanoic acid having a melting point range of 43 to 46 C. To thesolution of 32 grams of the above acid in 66 cc. of ethyl alcohol therewere added 6.8 grams of potassium hydroxide and 9.2 grams of thiourea,and the solution was refluxed until a crystalline mass was formed. Thiscrystalline mass was dissolved in 100 cc. of water containing 13.4 gramsof sodium bicarbonate and the mixture refluxed for two hours. Thesolution was then diluted with cold water and ice and made acid withdilute sulphuric acid. The 11- mercaptyl undecanoic acid was separatedby filtration and further purified by recrystallization from heptane.This purified acid had a melting point 01' 38 C. and was substantiallypure 11- mercaptyl undecanoic acid containing a very slight amount oflo-mercaptyl undecanoic acid. This acid was then esterified with ethylalcohol to form ethyl ll-mercaptyl undecanoate.

Alternatively, my polymerization regulator was also prepared by passinghydrogen bromide through a solution of about 20 grams of the ethyl esterof undecanoic acid in 250 cc. of benzene containing 5 drops 01 hydrogenperoxide. This solution was then washed thoroughly with water and twicewith a concentrated sodium bicarbonate solution and finally with saltwater. The solution 01 ethyl ll-bromo undecanoate containing arelatively small amount of ethyl lfl-bromo undecanoate was dried oversodium sulfate. The benzene was removed by distillation and the crudeester distilled at 1 mm. pressure. The crude ester was fractionated andthat fraction boiling at 128 to 134 C. at 1 mm. pressure was convertedto a mixture of ethyl ll-mercaptyl undecanoate and ethyl 10-mercaptylundecanoate. This conversion was eflected by dissolving 80 grams of theethyl bromo undecanoate, 20.8 grams of thiourea. and 5 drops ofconcentrated ammonium hydroxide in 125 cc. of ethyl alcohol.This'solution was refluxed for 3 hours and 39.6 grams of sodiumbicarbonate dissolved in 150 cc. of water was then added and refluxingcontinued for 30 minutes. The upper layer was separated and the lowerlayer was acidified with sulphuric acid and extracted '3 times with 20cc. portions of benzene. The upper layer and the benzene extracts werecombined and washed twice with salt water and dried over sodium sulfate.After removal of the benzene by distillation, the mercaptyl ester wasdistilled at 119 to 126 C. at 1 mm. pressure to purify the ester. Theresulting ester was actually a mixture of ethyl ll-mercaptyl undecanoateand ethyl IO-mercaptyl undecanoate with the first mentioned esterpredominating. The product of thissecond process contained a relativelylarger amount of ethyl lo-mercaptyl undecanoate than the ester preparedaccording tothe first process.

The following examples serve to illustrate the use of -my polymerizationregulators without limiting them to theparticular proportions oringredients. r

' Example 1 A synthetic rubber-like material was prepared as follows;

parts isoprene 20 parts alpha-methyl para-methyl-styrene 30 partsacrylonitrile 300 parts water 10 parts sodium stearate (emulsifyingagent) 1 part polymerization regulator 4 1 part potassium persuli'ate(polymerization catalyst) This polymerization regulator wassubstantially pure ethyl ll-mercaptyl undecanoate prepared as set forthin the first-mentioned process.

The emulsion was shaken for five days at 25 to 30 C. The emulsion wascoagulated with dilute acetic acid and the product in a yield of over90% was a plastic, easily milled material comparable to unvulcanizednatural rubber. This product ma be compounded and vulcanized in theusual manner.

Example 2 A synthetic rubber-like material was prepared as follows:

parts butadiene-L3 60 parts styrene 295 parts water 12 parts sodiumstearate 0.1 parts sodium hydroxide 1.2 parts potassium persulfate 1.2parts polymerization regulator The sodium hydroxide was for the purposeof placing the emulsion on the alkaline side. The polymerizationregulator was a mixture of ethyl ll-mercaptyl undecanoate and ethyl10-mercaptyl undecanoate prepared according to the second processhereinbefore described. The firstmentioned ester predominated in theregulator.

The emulsion was shaken for seven days at about 25 C. and thencoagulated with acetic acid. The product was comparable to unvulcanizednatural rubber and was more plastic than the usual butadiene-styrene(Buna S) synthetic rubber. This product may be vulcanized in the usualmanner.

Example 3 A synthetic rubber-like material was prepared as follows:

1200 parts isoprene 1800 parts water 36 parts sodium stearate 6 partsethyl ll-mercaptyl undecanoate 6 parts potassium persulfate 0.6 partsodium hydroxide The emulsion was shaken for 48 hours at a temperatureof 38 C. to 40 C. and then coagulated with dilute acetic acid. Theproduct was rubberlike, similar to unvulcanized natural rubber,relatively plastic and readily millable.

In general, my polymerization regulators produce tackier and morecohesive synthetic rubber-1ike materials and their use results in higherHaving described my invention in detail, it is obvious that variousmodifications may be made therein and that some features may be employedwithout others, all without departing from the spirit or scope of myinvention which is defined in the appended claims.

I claim:

1. The process which comprises polymerizing a material selected from thegroup consisting of an open chain, aliphatic conjugated diene containingi to 6 carbon atoms and a mixture of such a conjugated diene with adifferent copolymerizable compound containing a vinyl radical in anaqueous emulsion in the presence oi a polymerization regulator selectedfrom the group consisting of alkyl ll-mercaptyl undecanoate, alkyl-mercaptyl undecanoate, and a mixture of alkyl ll-mercaptyl undecanoateand alkyl IO-mercaptyl undecanoate, said alkyl radical having 1 to icarbon atoms inclusive.

2. The process which comprises polymerizing an open chain, aliphaticconjugated diene containing i to 6 carbon atoms and styrene in anaqueous emulsion in the presence of a polymeri= zation regulatorselected from the group consisting of alkyl l1-mercaptyl undecanoate,alkyl 10- mercaptyl undecanoate, and a mixture of alkyl ll-mercaptylundecanoate and alkyl lo-mercaptyl unclecanoate, said alkyl radicalhaving 1 to a carbon atoms inclusive.

3. The process which comprises polymerizing an open chain, aliphaticconjugated diene containing 4 to 6 carbon atoms and acrylonitrile in anaqueous emulsion in the presence of a polymerization regulator selectedfrom the group consisting of alkyl ll-mercaptyl undecanoate, alkyllfl-mercaptyl undecanoate, and a mixture of alkyl ll-mercaptylundecanoate and alkyl lfl-mercaptyl undecanoate, said alkyl radicalhaving 1 to 4 carbon atoms inclusive.

4. The process which comprises polymerizing butadiene-LB, and acopolymerizable compound containing a vinyl radical in an aqueousemulsion in the presence of a polymerization regulator selected from thegroup consisting of alkyl 11- mercaptyl undecanoate, allwl IO-mercaptylundecanoate, and a mixture of alkyl ll-mercaptyl undecanoate and alkylIO-mercaptyl undecanoate,

said alkyl radical having 1 to 4 carbon atoms inthe presence of apolymerization regulator selected from the group consisting of alkyl 11-mercaptyl undecanoate and alkyl lo-mercaptyl undecanoate, and a mixtureof alkyl ll-mercaptyl undecanoate and alkyl 10-mercaptyl undecanoate,said alkyl radical having 1 to 4 carbon atoms inclusive.

6. In the process of polymerizing an open chain, aliphatic conjugateddiene containing 4 to 6 carbon atoms in an aqueous emulsion, the step ofeffecting the polymerization in the presence of a polymerizationregulator selected from the group consisting of alkyl ll-mercaptyl undecanoate, alkyl lO-mercaptyl undecanoate, and a mixture of alkylll-mercaptyl undecanoate and alkyl IO-mercaptyl undecanoate, said alkylradical having 1 to 4 carbon atoms inclusive.

7. In the processof polymerizing butadiene-l,3, in an aqueous emulsion,the step of conducting the polymerization in the presence of apolymerization regulator selected from the group consisting of alkylll-mercaptyl undecanoate, alkyl IO-mercaptyl undecanoate, and a mixtureof alkyl ll-mercaptyl undecanoate and alkyl 10- mercaptyl unclecanoate,said alkyl radical having 1 to 4 carbon atoms inclusive.

8. The process which comprises polymerizing a material'selected from thegroup consisting of an open chain, aliphatic conjugated diene containing4 to 6 carbon atoms and a mixture of such a diene with a differentcopolymerizable compound containing a vinyl radical in an aqueousemulsion in the presence of a polymerization regulator selected from thegroup consisting of alkyl ll-mercaptyl undecanoate, alkyl IO-mercaptylundecanoate, and a mixture of alkyl ll-mercaptyl undecanoate and. alkyl10- mercaptyl undecanoate, said alkyl radical having 1 to 4 carbon atomsinclusive, said regulator being present in an amount less than 1% byweight based on the total weight of monomeric polymerizable material.

9. The process which comprises polymerizing butadiene-1,3 and styrene inan aqueous emulsion in the presence of ethyl ll-mercaptyl undecanoateand ethyl IO-mercaptyl undecanoate.

' KARL H. WEBER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,378,030 Olin June 12, 19452,402,644 Lazier et a1 June 25. 1946

1. THE PROCESS WHICH COMPRISES POLYMERIZING A MATERIAL SELECTED FROM THEGROUP CONSISTING OF AN OPEN CHAIN, ALPHATIC CONJUGATED DIENE CONTAINING4 TO 6 CARBON ATOMS AND A MIXTURE OF SUCH A CONJUGATED DIENE WITH ADIFFERENT COPOLYMERIZABLE COMPOUND CONTAINING A VINYL RADICAL IN ANAQUEOUS EMULSION IN THE PRESENCE OF A POLYMERIZATION REGULATOR SELECTEDFROM THE GROUP CONSISTING OF ALKYL 11-MERCAPTYL UNDECANOATE, ALKYL10-MERCAPTYL UNDECANOATE, AND A MIXTURE OF ALKYL 11-MERCAPTYLUNDECANOATE AND ALKYL 10-MERCAPTYL UNDECANOATE, SAID ALKYL RADICALHAVING 1 TO 4 CARBON ATOMS INCLUSIVE.